1. Field of the Invention
This invention relates to an assembly which will lock one drill string to another and form a pressure seal.
2. Prior Art
The present invention is a device which can be installed in the annulus between two coaxial drill strings and will; lock one string, in tension, with regard to the other, form a pressure tight seal, and center one string with the other. The device may be used in most drilling operations, however, it is particularly suitable for use in offshore drilling installations.
In any drilling operation it is possible to have some impairment occur which limits the ability to continue drilling operations, this is commonly referred to as losing the hole. However, in offshore drilling this problem is compounded due to the large distance between the drilling platform and the ground surface, or mudline. If some disaster or problem arises which causes the hole to be lost, the capability of recovering the hole must exist. Thus, in most offshore drilling operations a large first casing is drilled to a given depth below the mudline, then a second smaller casing is drilled through the first larger casing to a greater depth, a third and smaller casing may then be used to drill to any given depth through the first and second casings. The present invention is used to secure and seal the first two casings one to the other. The present invention is placed immediately after the second casing is drilled into its final position and remains in position until it is no longer needed.
In the drilling industry there exists many prior art methods for packing off (sealing) one portion of a casing, or for sealing one casing off with respect to the other. However, these devices serve only to provide a seal and do not secure one casing to the other. A separate problem is that prior art devices are not recoverable and when positioned, become a permenant part of the casing. There also exists devices for centering one string of casing with respect to the other, however, the device does not secure one string to the other, nor pack off the annulus.
The present invention attempts to solve these problems by providing a device which will pack off, center and secure one coaxial string of casing to the other. An additional feature is that the device is retrievable and may be reused.